Indicator



June 15, .1943.

R. 1:. CONOVER 1, 1

INDICATOR' Filed June 17, 1940 4 Sheets-Sheet l [III III,

TIME

lural:

June 15, 1943.

R. E. CONOVER 2,321,581

INDICATOR Filed June 17, 1840 4 Sheets-Sheet 2 35. 4 JJEL4b 17/67/420 5. Cyo 145,

aways 4 Sheets-Sheet 5 we V0096: \9UPPLY R. E. CONOVER INDICATOR Filed June 17, 1940 June 15, 1943.

I P/chwep 15.

4 Sheets-Sheet 4 R. E. CONOVER v INDICATOR Filed June 17, 1940 June 15, 1943;

Patented June 15, 1943 UNITED- STATES, PATENT OFFICE 8 Claims.

Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to a method of and apparatus for determining the frequency and phase characteristics of a repeating function, especially as compared with a selected standard, and has particular utility in the synchronization of the motions of rotating or reciprocating elements.

It is often desirable to know the exact instantaneous corelation between certain repeating functions, such as rotating or reciprocating machine elements, engines, and the like. It may be necessary only to cause the speed of one such element, or engine, to closely approach the speed oi another element or.machlne, considered for the moment as a standard. In other cases it may be necessary to cause both elements to oper-- ate at exactly the same speed, or frequency, but

without regard to phase difierence. In still other cases it may be desired or necessary to cause two or more such elements to operate not only at the same speed, but in a particular phase relationship.

In the operation of multiengined airplanes, for example, it is often desirable to know the relative speeds of all engines with respect to each other to a more exact degree of accuracy than is possible with standard tachometers. This comparison is necessary in order to check the operation of automatic synchronizing devices, or to assist in setting the engines by manual control.

It is, therefore, the general object of the present inventicn'to provide a novel method and apparatus for determining the instantaneous relative frequency and phase characteristics of a repeating function with respect to another similar repeating function or some other standard of comparison.

A further object is to provide a novel method and apparatus for indicating exact synchronisa- "on of two or more engines and determining ill'erence in speed.

require the addition of equipment to the engines to be compared.

s A still further object is to provide means for generating a potential of saw-tooth wave form, and having a frequency controlled by the frequency of a repeating function to be studied.

These and other objects will become apparent to one skilled in the art as the description proceeds in connection with the accompanying drawings.

In the drawings: Figure 1 is a wiring diagram of a fundamental circuit illustrating the principles of the present invention;

A further object is to provide an indicating f Figure 2 shows the saw-tooth wave form which is developed in the circuit of Figure 1;

Figure 3 shows the approximate wave form that appears onthe primary side of a magneto;

Figures 4a to 4e, inclusive, show patterns that appear on the cathode ray osciliograph for various phase angle relations between two engines where EeJs the potential across condenser I, E is the voltage across the battery 3, e is the constant, 2.718, t is the time, R is the resistance of the resistor 2, and C is the capacitance of condenser i. This equation is-illustrated graphically in Figure 2 by the curve Ee- The condenser i is then discharged through an ignition-controlled gas triode, or other electronic tube or relay device, such as the""l' hyratron 4, and the resistor I. By choosing the constants of the circuit such that the condenser is charged only on the lower part of the curve lo, a saw-tooth wave form may be developed as illustrated by the full linelinl'lgurel Discharge occurs through the plate circuit of the tube l and the resistor I,

the time oi discharge occurring at some point.

such a; i, which is relatively low on the curve Ee. so that the charging line I will he silhstan tially a'straight line. The constants of the circult are also such that the lower portion of the curve Ec has considerable slope, as shown, and the duration of the discharge is very short with respect to the charging time, thus making the discharge line 8 also substantially a straight line and lying substantially vertically beneath the point 6. In operation, this wave form is repeated so that it resembles a saw-tooth form as shown.

The time of discharge, or the point 6, is controlled by the engine, in the present instance, through the tube 4, directly in response to the breaker on the engine magneto. In Figure l the structure included by the legend Engine A includes the primary coil II, the secondary coil I2 and breaker I3. The voltage curve existing across the primary ofa typical magneto i illustrated in Figure 3, the voltage peaks I4 and I5 occurring at the time of separation of the breaker contacts I3. Because of the fact that the magneto generates an alternating current voltage, every other voltage peak, such as I4, is positive, and every other peak, such as I5, is negative. The grid I6 of the tube 4 is normally biased at a high negative potential by a source of voltage, such as a battery II. This potential is of a sufliciently high value to prevent discharge of the condenser through the tube 4 until such time as a peak value of positive voltage I4 from the magneto exceeds or bucks out the voltage supplied by the battery II. Discharge of the condenser I then takes place through the local circuit, consisting of the resistor 5, the plate IB, and the cathode I9, back to the negative side of the condenser.

It will be apparent then that a discharge takes place on every positive peak I4 of primary magneto voltage, the negative peaks I5 having no effect on the tube 4. For a four-cycle engine, the number of discharges per minute is equal to:

Number of cvlinriers *2-(R. P. hi.) because each cylinder fires only once in every other revolution, and only half of these ignitions are at positive voltage peaks. The above equation may be expressed in more general form as follows:

Time in seconds between positive 60 peaks (It. i. M.) N where N is the number of breaks made by the engine magneto in each revolution. The primary voltage curve on a typical engine magneto was found to have peak values of at least 100 volts. By using a high negative grid bias. the tips of the positive peaks can be made to trip the triode tube 4 directly, thus eliminating the necessity for accessory contactors. If the values of the resistor 2 and condenser I are chosen so that the time constant of the combinationas expressed by the formula t=RC'--is considerably greater than the interval between positive peaks I4 at the slowest speed for which synchronization is desired, then the slope of line I will be substantially straight at all operating speeds. As the engine speed is increased, the amplitude of the saw-tooth wave form F will decrease slightly because of the decreased time allowed for charging. This variation in amplitude has no efiect on the operation of the indicator. At the higher engine speeds the time interval will also be less, thus producing a higher frequency in the saw-tooth wave form, the frequency being proportional to the engine speed.

The value of the resistance 5 should be such as to limit the value of the discharge current through the tube 4 to conform with the allowable ratings. The resistor 22 limits th grid current of the tube 4 to a safe value when the high voltage peaks I4 are impressed thereon.

The voltage across the condenser I is applied to one pair of deflecting plates 23 of a cathode ray oscillograph through a coupling condenser 24, the resistor 25 being in parallel circuit as illustrated. A similar voltage, generated by a second, exactly identical circuit tripped by a magneto on another engine, such as Engine B, is applied to the other pair of deflecting plates 26, preferably arranged at right angles to the first pair of plates 23. In the second circuit the condenser Ia. corresponds to the condenser I, the resistance 2a corresponds to the resistance 2, etc., battery 3 being used to energize both circuits. All corresponding elements in the two circuits bear like numerals in their reference characters.

The embodiment illustrated by wiring diagram in Figure 1 has been successfully operated, using a value of 1 m. f. for the condenser I, a value of 1 megohm for the resistance 2, and a value of 500 ohms for the resistance 5, the tube 4 being a conventional hot cathode Thyratron.

When two saw-tooth wave forms are applied to the oscillograph as described above, there will be produced on the screen a pattern closely resembling one of the patterns illustrated in Figures 4a to 4c. The writing speed of the cathode ray beam on the portion 1 of the saw-tooth wave form is much slower than the writing speed on the portion 8; therefore, the intensity of the portion 1 is much greater than that of the portion 3. The average intensity of the tube can be adjusted so that the portion I will be visible while the portion 8 will be invisible. In Figures 4a to 4c the heavy lines represent the slow writing speed, while the light lines represent the fast writing speed.

Assuming that the magnetos in engine A and engine B are firing at the same instant, the two saw-tooth voltage curves applied to deflecting plates 23 and 26 will be in phase, and the pattern resulting on the screen of the oscillograph tube will be a straight line, as illustrated in Figure 40.

- The tube is illustrated in Figures 4a to 4e as being rotated so that the deflecting plates are each at an angle of 45 with the horizontal, with the result that the straight-line pattern 29 in Figure 4a, illustrating the condition of in-phase synchronism, will be horizontal, occupying the center of the screen. The condition of in-phase synchronism being a special case, this horizontal line 29 can be considered as the vector sum of two portions 1 of the saw-tooth wave form of Figure 2 superimposed on the vector sum of two portions 8.

Figure 4?) illustrates the pattern resulting ii the magnetos on the two engines, A and B, are assumed to fire out of phase with respect to the saw-tooth wave form F. The heavy line 30 may be considered to be traced in response to the portion 1 of the saw-tooth wave form from engine A acting in conjunction with the corresponding portion of the saw-tooth wave form generated by the engine B. The ray in the oscillograph moves under the influence of forces between both pairs of deflecting plates 23 and '26, and point 3| may then be said to represent the peak 6 of the saw-tooth wave f rm from engine A. The discharge portion 8 from the condenser I, produced by the engine A, is represented by a thin line or path 32, at which time the cathode ray is moving very swiftly under the influence of deflecting plates 23 in response to the discharge of the condenser I, and relatively slowly in a direction between the plates 26 in response to the charging part of the curve 1 from engine B, since engine B is assumed to lag 90 degrees behind engine A. With respect to time, the point 33 is reached so quickly after the point 3| that the path of the line 32 on the screen is practically invisible. having discharged, begins another charge on the line I, and this part of the curve, inconjunction with the remainder of the first charging curve I for the condenser Ia, will produce a line 34 parallel to line 30. When the potential across condenser Ia reaches the point 6 and the condenser la is then discharged, the cathode ray will move rapidly from the point 35 along the line 36 to the point 31 to begin another cycle. The path 36 will be traced faintly on the oscillograph screen similarly to the path 32, so that the complete pattern will appear to consist solely of a long stationary horizontal line 30 and a short stationary horizontal line 34, as long as the engines A and B are running-90 out of phase at the same speed.

Figure 40 illustrates the pattern on the oscillograph screen when the two'engines are running at the same speed 180 out of phase with respect to the saw-tooth wave form F. The elements of this pattern are traced in the same se quence as the pattern described in Figure 4b but the proportions are different, the pattern being substantially symmetrical above and below itsmid-point because-the second condenser Ia begins to charge at a phase angle of 180 after condenser I begins to charge. The line 30 in Figure 40 therefore represents the final part of the charging curve of condenser I and the first part of the charging curve of condenser Ia. Similarly, the line 34 represents the final part of the charging curve of condenser Ia and the first part'of the charging curve of condenser I at the beginning of its next cycle. Figure 4d illustrates the appearance of the oscillograph pattern for a phase angle difierence of 270, and

-it has the appearance of Figure 4b inverted.

After engine B has slipped 360 electrical degrees with respect to engine A, as determined from the relationship of the respective saw-tooth wave forms, the magnetos will again be firing at the same instant and the oscillograph will indicate a condition of synchronism such as illustrated in Figure 4e, which is seen to be identical with Figure 4a.

In order for the phase angle to change, it is of course necessary for engine B to revolve either slower or faster than engine A; and when this occurs, the complete progression of patterns from Figure 4a through Figure 4e will be created either in the sequence illustrated or in the reverse sequence, the patterns of course changing gradually and progressively from one to the next. Under the specific set of conditions assumed in the discussion of Figures 4a through 4ethat is, that engine B was lagging behind engine A-the long line 29 of Figure 4a will appear to move downwardly in the oscillograph screen and become shorter. After a small amount of movement, it will appear in the position and length of line 30 in Figure 4b, and the shorter line, indicated at 34, will 'make its appearance at the top of the oscillograph screen. With a further angle of slip, as described in connection with Figure 4c, the lower line 30 will have dropped to a still lower position on the oscillograph screen The condenser I, now

and its length will have been still further reduced. At the same time, the upper line 34 will have increased in length and will have descended until it is symmetrical in size and position with the line 30. When the lag in engine B has produced a still greater angle of slip, as illustrated in Figure 4d, the lower line 30 will be seen to With the type of saw-tooth Wave form illus- 1 trated in Figure 2, the discharge line 8 from each condenser will descend so steeply that an operator will probably be unable to observe the extremely rapidly traced paths 32 and 36. What th operator will actually see, when engine B is turning slower than engin A. will be two horizontal lines descending across the screen of the oscillograph, and he will be able to calculate the diiference in speed of the two engines from the fact that the time required for any particular pattern to reappear will represent the time inierval between identical phase relationships of the saw-tooth wave forms and, consequently, of the two positive voltage peaks I4 in Figure 3. It is noted that this interval does not represent a. difference of one revolution of the engine shafts, except in the special case where there would be only one positive wave peak I4 for each revolution. If the two engines are runn ng at the same speed, the pattern will be stationary--that is, the lines 30 and 34 will have no relative movement across the oscillograph screen. If it is necessary only to maintain two engines at the same speed, regardless of phase angle difference, the operator is required only to regulate the speed of one of the engines until the pattern on the oscillograph screen ceases to move either up or down. If it is desired not only to make the speeds of .both engines the same. but tr:- bring them in. the same phase relationships with regard to the firing of the respective ignition systems, then it will be necessary to adjust the speed of one of the engines until the straight line pattern of Figure 4a or.Figure 4e is produced.

The arrangement of the circuit of Figure 1 has been slightly modified in Figure 5 in order that a common high voltage supply may be used to supply the voltages supplied in. Figure 1 b.v the two batteries 3 and I1, and also to furnish the necessary voltages for the cathode ray tube. Employing the'same reference numcrals in Figure 5 to denote similar elements in Figure l, the resistor 2 now servcs the'dual function of acting as charging resistance and also furnishes the bias voltage for the tube 4. The constants of the circu t are such that at the be n i f 1h: charging of cndenser I from the high volage supply, the total voltage exis s across the resistor 2, making the ne ative bias very high. As the charge on the condenser I increases. the voltage across resistor 2 decreases. By th time the magneto fires, the voltage across resistor 2 isdecreased to a value low enough to permit the positive peak I4 to overcome the existing b as at that time. al -rwing the tube 4 to disrharge the condenser. The r sistor 4| and potentiometers 42 and 43 are the usual controls for the electron beam in the cathode ray tube (not shown in Figure 1). The numeral 44 is used to represent the cathode ray tube circuit as a whole. In other respects the identical twin circuits in Figure correspond to those of Figure 1 and produce both the same type of saw-tooth wave form across the condensers I and la and the same type of pattern on the oscillograph screen.

The circuit shown in Figure 6;is an alternative methodof timing the discharge of tube 4. This circuit is applicable where a magneto to furnish the positive peaks is not available, and is therefore usable on any rotating or reciprocating mechanism or other repeating function or cycle. The repeating function or cycle in Figure 6 is embodied in a rotating disc 50, carrying a contact 5| which makes momentary contact with a brush 52, thereby applying voltage across the resistor 53. Such contact effects connection between the grid I6 of the tube 4 and the positive' end of the resistor 53 on the one hand, with the positive side of the high voltage supply on the other hand, thereby rendering the tube 4 conductive and permitting the discharge of the condenser I therethrough. When the contact elements SI and 52 separate,'the grid vHi is held at the negative potential of the negative side of the high voltage supply through the resistors 22 and 53. The contacts 5| and 52 may be operated either by rotating or reciprocating means or by any other function, the nature of which is desired to be indicated or studied. In other respects, the circuit of Figure 6 is similar to the embodiments previously described. It is understood that the other pair of deflecting plates 26 would be connected in another circuit similar to the one shown or to some other standard of comparison for the saw-tooth wave form generated by the circuit shown.

Figure 7 is an expansion of the circuit of Figure 5 as it would be applied according to the teachings of the present invention to a four-engined airplane. In such an installation it is desirable to be able to synchronize three of the engines with respect to the other engine, and it is also desirable to be able-to select any one of the four engines as the master in case of failure of one engine. A four-circuit, four-position multi-contact switch 60 is provided to make this selection. In other respects the circuit of Figure 7 corresponds to that of Figure 5, the wiring diagram merely being expanded to show the duplication of circuits required to serve all four engines. The principles of the invention could, of course, be applied by anyone skilled in the art to any number of engines or repeating functions to be compared. It is also to be understood that it is not necessary that the engines or other repeating functions be equipped with magnetos, since the contact device and the biasing resistor arrangement shown and described in Figure 6 may be substituted for each of the magneto and breaker units shown in Figure 7. Figure 7, in addition, discloses a separate filament voltage source for energizing the filaments of all the thyratrons and all the oscillograph tubes. In practice the high voltage supply may conveniently be supplied by a dynamotor, the primary of which is directly connected across the filament supply. The'filament circuits are well understood in the art and will not be described in detail. In Figure '7 the elements common to previously described embodiments are supplied with reference characters having the same numerals.

Thus, it will be seen in Figure '7 that the defleeting plates 23, in each of the oscillographs A, B, C, and D, are connected with a saw-tooth wave form circuit from a different engine, the oscillograph A having its plates 23 connected with the engine A, the oscillograph B having its plates 23 connected with the engine B, etc. By adjusting the switch Bl] to the selected station a, b, c, or d, any one of the engines may be made the master for purposes of comparison in all of the oscillographs. In applications where it is not necessary to be able to select the master engine, three cathode ray oscillograph tubes can be used instead of four.

In certain applications it may be desired to synchronize all engines with respect to a motordriven master synchronizer. In such cases the circuit shown in Figure 6 may be used in conjunction with the master synchronizer by mounting the contact wheel 50 on the motor shaft of the master synchronizer.

While applicant has illustrated the principles of his invention as applied in'various embodiments to a multiengined airplane or the like, it is to be understood that the invention is not intended to be limited thereto, since, as previously pointed out, the present invention is of utility in comparing all types of repeating functions, whether or not these functions may be associated with revolving or reciprocating parts. It is also to be understood that changes and modifications may be made in the present disclosure and that certain features of the invention may be used alone or in combination, within the scope of the appended claims. For example, the repeating wave form F in Figure 2 need not necessarily be of the specific saw-tooth shape illustrated. The charging line I might be made steep, and the discharge line 8 sloping, or the shape of the curve may be otherwise modified, providing that two such wave forms will produce significant patterns when combined in an indicator such as a cathode ray oscillograph or the like. It is also within the scope of the present invention to use dissimilar wave forms which will produce significant patterns and to use some other form of indicator for combining and comparing the frequencies of the two wave forms.

Having now described my invention and in what manner the same may be used, what I claim as new and desire to secure by Letters Patent is:

1. In an indicating device for comparing speed and phase relationships of two repeating functions, a pair of rotatable shafts; a first relay device normally maintained in nonconducting condition; a first condenser adapted to discharge through said relay device when said first relay device is rendered conductive; means associated with one of said shafts to render said relay device conductive periodically in proportion to the speed and phase angle of said one shaft; a cathode ray oscillograph having two pairs of deflecting plates, one of said pairs of plates having the potential of said first condenser applied thereacross; a second relay device normally maintained in nonconducting condition; a second condenser adapted to discharge through said second relay device when said second relay device is rendered conductive; means for charging and discharging each of said condensers under the, control of its respective relay device; and means associated with the other of said shafts to render said second relay device conductive periodically in proportion to the speed and phase angle of said other shaft, the potential across said second condenser being applied across the other pair of said deflecting plates.

2. In an indicating device for comparing speed and phase relationships of two repeating functions, a cathode ray oscillograph having two pairs of deflecting plates capable of producing a pattern on the screen of said oscillograph, each pair of deflecting plates having applied thereto the potential existing across one of two independently responsive condensers, respectively, and means to charge and discharge each of said condensers cyclically as an incident of one of two independent repeating functions so as to develop a saw-tooth voltage curve with respect, to time for each of said functions corresponding to phase and frequency characteristics of the respective- 3. In a device for indicating the relationship of two independent repeating functions, an electrical valve and a condenser associated with one of said functions; an electric valve and a condenser associated with the other of said functionsmeans for charging and discharging each of said condensers under the control of its respective .to effect the discharge of its associated condenser with a frequency proportional to'the frequency and phase angle of the associated repeating function; and a cathode ray oscillograph having two pairs of deflecting plates, one pair of plates being influenced by the potential across one of said condensers, and the other pair of plates being influenced by the potential across the other condenser.

4. In an indicating device for comparing speed and phase relationships of two repeating functlons, a cathode ray oscillograph having two pairs of deflecting plates capable of producing a pattern on the screen of said oscillograph, a plurality of independent saw-tooth wave generators, each f whichis associated with one of said pairs of plates, each of said generators being responsive cyclically to a separate repeating function, the time of response being indicative of speed and relative position of its respective associated repeating function, each pair of deflecting plates being associated with one of said generators whereby a pattern will be produced on said oscillograph indicative of differences in speed and circuits for moving said indicator in one direcrelative position between the respective repeating functions.

5.Means for simultaneously indicating the speed and phase relationships of two rotating elements, comprising a plurality of electrical circuits each of which is separately associated with one of said elements,'means associated with one of said elements to create an electrical impulse periodically in one of said respective circuits in proportion to the speed and phase angle of said one of said elements, means associated with the other of said elements to create an electrical impulse periodically in the other of said circuits in proportion to the speed and phase angle of said other of said elements, an indicator capable of tracing a visible'pattern, means actuated through said one of said circuits for moving said indicator in one direction, means actuated through said other of said circuits for moving said indicator in another direction, whereby said indicator will trace a pattern of constantly changing form when said elements are rotating at different speeds, and a stationary, repeating pattern when said elements are rotating at the same speed, each circuit comprising a condenser, an electronic discharge tube having a plate circuit in parallel with said condenser, a resistance in series with said plate circuit and the negative side of said condenser; a grid element in said tube; a single source of supply voltage for charging said condenser, for establishing a plate voltage, and for establishing a grid potential; and means operated by the respective repeating function for altering said grid potential to render said tube of the respective circuit conducitve to discharge the respective condenser, said grid being maintained at a blocking potential until altered by said respeclive means, said resistance having a value such that when said respective condenser begins to charge, substantially the total voltage of said supply exists across said resistance, and as the charge in said condenser increases, the voltage across said resistance decreases to a value which will make said tube responsive to said means.

6. An indicating device as claimed in claim 2 wherein an electrical circuit is provided for each condenser, each circuit including an electrical valve and a resister, and wherein the value of the constants in each circuit is such that the respective condenser will be charged only on the lower part of the charging curve.

7. Means for simultaneously indicating the speed and phase relationships of two rotating elements, comprising a plurality of electrical circuits each of which is separately associated with one of said elements, means associated with one of said elements to create an electrical impulse cally in the other of said circuits in proportion to the speed and phase angle of said other of said elements, an indicator capable of tracing a visible pattern, means actuated through said one of said tion, and means actuated through said other of said circuits for moving said indicator in another direction, whereby said indicator will trace a pattern of constantly changing form when said elements are rotating at different speeds, and a stationary, repeating pattern when said elements are rotating at the same speed, each circuit comprising a condenser, an electronic tube having a plate circuit connected across said condenser and adapted to discharge said.condenser when said plate circuit is rendered conductive, a direct current voltage source for charging said condenser, said tube having a grid connected with the negative side of said voltage source through a resistance and adapted to render said tube non-conductive, and means operated by said repeating function to connect said grid to the positive side of said voltage source so as to render said tube conductive to discharge said condenser.

8. Means for simultaneously indicating the speed and phase relationships of two rotating elements, comprising a plurality of electrical circuits each of which is separately associated with one of said elements, means associated with one of said elements to create an electrical impulse periodically in one of said respective circuits in proportion to the speed and phase angle of said elements, means associated with the other of said elements to create an electrical impulse periodically in the other of said circuits in proportion to the speed and phase angle of said other of said elements, an indicator capable of tracing a visible pattern, means actuated through said one of said circuits for moving said indicator in one direction, and means actuated through said other of said circuits for moving said indicator in another direction, whereby said indicator will trace a pattern of constantly changing form when said elements are rotating at difierent speeds, and a stationary, repeating pattern when said elements are rotating at the same speed, each circuit comprising a condenser, means to charge said condenser at a predetermined rate, means to discharge said condenser at a rate greatly in excess of the rate of charge, said discharge means comprising the plate circuit of an electronic tube, a grid in said tube normally maintained at a blocking potential to render said plate circuit nonconductive, and means operated by said repeating function to overcome said blocking grid potential and render said tube conductive to discharge said condenser periodically in proportion to the fre- 10 quency and phase of said repeating function.

RICHARD E. CONOVER. 

